A meta-analysis of walnuts by Harvard scientists has found diets rich in walnuts can significantly reduce cholesterol levels, supporting growing evidence to suggest these popular nuts can improve healthy blood lipid ratios.

In their investigation of thirteen studies, the researchers demonstrated that walnut-rich consumption decreased total and low-density lipoprotein (LDL) cholesterol during short term trials.

However the scientists suggested that "larger and longer-term trials" are needed to observe the effects of eating walnuts, rich in polyunsaturated fatty acids, on cardiovascular risk and weight management.

Their analysis joins a blossoming body of science that has linked nut consumption – including almonds and macadamias – to improvements in markers of cardiovascular health.

Coronary heart disease places a significant financial burden on all European states, and in the UK alone costs the health system more than €5bn per year. Governments, scientists and the food industry itself continue to invest time and money in pinpointing potential dietary solutions that could boost cardiovascular health.

Design of the meta-analysis

Published in a recent issue of the American Journal of Clinical Nutrition, researchers Deirdre Banel and Frank Hu conducted the meta-analysis to, "estimate the effect of walnuts on blood lipids".

Literature databases were searched for published trials that compared a specifically walnut-enhanced diet with a control diet.

"We conducted a random-effects meta-analysis of weighted mean differences of lipid outcomes," said the scientists.

The13 studies selected represented some 365 participants, with diets lasting between four and 24 weeks and walnuts providing between 10 and 24 per cent of total calories.

"When compared with control diets, diets supplemented with walnuts resulted in a significantly greater decrease in total cholesterol and in LDL-cholesterol concentrations," the Harvard researchers wrote.

Further, the meta-analysis results gave a nod to the widening circle of potential health benefits contained in walnuts.

A meta-analysis of walnuts by Harvard scientists has found diets rich in walnuts can significantly reduce cholesterol levels, supporting growing evidence to suggest these popular nuts can improve healthy blood lipid ratios.